1
general::
Suddenly become angry, as in She flared up at the slightest provocation. This metaphoric expression, dating from the mid-1800s, transfers a sudden burst of flame to sudden rage.
American Heritage Idioms
2
general::
Phrase(s): flare up
1. Lit. [for something] to ignite and burn. • The firewood flared up at last—four matches having been used. 2. Lit. [for a fire] to burn brightly again and expand rapidly. • After burning quietly for a while, the fire suddenly flared up and made the room very bright. 3. Fig. [for a pain or medical condition] to get worse suddenly. • My arthritis flares up during the damp weather. 4. Fig. [for a dispute] to break out or escalate into a battle. • A war flared up in the Middle East. • We can’t send the whole army every time a dispute flares up. 5. and flare up at someone or something Fig. to lose one’s temper at someone or something. • I could tell by the way he flared up at me that he was not happy with what I had done. • I didn’t mean to flare up.
McGrawhill's American Idioms And Phrasal Verbs